1. Field of the Invention
The present invention relates to a so-called tandem type image forming apparatus capable of performing color printing.
2. Description of the Background Art
Conventionally, a so-called tandem type image forming apparatus 100 capable of performing color printing as shown in FIG. 4 has been known. The image forming apparatus 100 includes plural photoconductive drums 101 for respective colors aligned side by side (yellow drum 101Y, magenta drum 101M, cyan drum 101C, and black drum 101K), and a transfer belt 104 disposed beneath the respective photoconductive drums 101 and turning around a pair of side rollers 102 and 103. The surface of an upper side 104a of the transfer belt 104 abuts on the peripheral surfaces of the respective photoconductive drums 101. At a center portion of a lower side 104b of the transfer belt 104, an intermediate roller 105 and a transfer roller 106 disposed oppositely to the intermediate roller 105 via the transfer belt 104 are provided. A charger, an exposing device, a developing device, a cleaning device, and so forth are provided on the periphery of each photoconductive drum 101, all of which are omitted in FIG. 4.
As the transfer belt 104 turns, toner images on the photoconductive drums 101 for respective colors are superimposed one on another on the surface thereof to form a color image. A recording sheet P is sent from a sheet cassette 107 to a nip portion between the intermediate roller 105 and the transfer roller 106 in synchronism with an action that a portion of the transfer belt 104 bearing the color image thus formed passes by the nip portion. The color image formed on the surface of the transfer belt 104 is thus transferred onto the recording sheet P. The recording sheet P done with the transfer processing is then subjected to fixing processing by heating for the toner image in a fixing device 108 provided directly downstream from the nip portion. Subsequently, the recording sheet P is discharged toward a sheet discharge tray 100a. 
In the image forming apparatus 100 configured as above, each photoconductive drum 101 is heated due to application of a voltage from the charger and irradiation of a laser beam from the exposing device. In some cases, the transfer belt 104 is overheated when heat is transmitted from the respective photoconductive drums 101 or when it is irradiated to radiation heat generated in the fixing device 108. When the transfer belt 104 is overheated, there occurs an inconvenience that toner particles on the transfer belt 104 melt and are firmly fixed onto the transfer belt 104. Further, it is no longer possible to apply cooling processing to the photoconductive drums 101 via the transfer belt 104, which causes another inconvenience that image forming processing on the peripheral surfaces of the photoconductive drums 101 is adversely affected.
In order to prevent the occurrence of such inconveniences, it has been known to provide a cooling mechanism, in which a cooling fan 109 is disposed in close proximity to the lower side 104b and outside air taken in by the driving of the cooling fan 109 is blown on the surface of the lower side 104b. An image forming apparatus provided with such a cooling mechanism is disclosed, for example, in JP-A-2001-296755, JP-A-2003-29540, and JP-A-2004-361626.
In the image forming apparatus 100 shown in FIG. 4, however, the intermediate roller 105 and the transfer roller 106 are provided at the center portion of the lower side 104b of the transfer belt 104. Because these rollers 105 and 106 block air sent from the cooling fan 109, it is possible to supply only a half of the lower side 104b with the air sent from the cooling fan 109. Hence, the cooling mechanism in the conventional art has a problem that it fails to apply the cooling processing to the transfer belt 104 effectively.